A variety of respiratory masks are known which have flexible seals that cover the nose and/or mouth of a human user and are designed to create a continuous seal against the user's face. Because of the sealing effect that is created, gases may be provided at positive pressure within the mask for consumption by the user. The uses for such masks range from high altitude breathing (i.e., aviation applications) to mining and fire fighting applications, to various medical diagnostic and therapeutic applications.
One requisite of such respiratory masks has been that they provide an effective seal against the user's face to prevent leakage of the gas being supplied. Commonly, in prior mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort for the user. This problem is most crucial in those applications, especially medical applications, which require the user to wear such a mask continuously for hours or perhaps even days. In such situations, the user will not tolerate the mask for long durations and optimum therapeutic or diagnostic objectives thus will not be achieved, or will be achieved with great difficulty and considerable user discomfort.
The prior art includes at least two types of respiratory face masks for the types of applications mentioned above. The most common type of mask incorporates a smooth sealing surface extending around the periphery of the mask and exhibiting a generally uniform (i.e, predetermined or fixed) seal surface contour which is intended to be effective to seal against the user's face when force is applied to the mask with the smooth sealing surface in confronting engagement with the user's face. The sealing surface may consist of an air or fluid filled cushion, or it may simply be a molded or formed surface of a resilient seal element made of an elastomer such as plastic or rubber. Such masks have performed well when the fit is good between the contours of the seal surface and the corresponding contours of the user's face. However, if the seal fit is not good, there will be gaps in the seal-to-face interface and excessive force will be required to compress the seal member and thereby attain a satisfactory seal in those areas where the gaps occur. Such excessive force is unacceptable as it produces high pressure points elsewhere on the face of the user where the mask seal contour is forcibly deformed against the face to conform to the user's facial contours. This will produce considerable user discomfort anywhere the applied force exceeds the local perfusion pressure, which is the pressure that is sufficient to cut off surface blood flow. Ideally, contact forces should be limited between the mask and the user's face to avoid exceeding the local perfusion pressure even at points where the mask seal must deform considerably.
The problem of seal contact force exceeding desirable limits is even more pronounced when the positive pressure of the gas being supplied is relatively high or is cyclical to high levels. Since the mask seals by virtue of confronting contact between the mask seal and the user's face, the mask must be held against the face with a force sufficient to seal against leakage of the peak pressure of the supplied gas. Thus, for conventional masks, when the supply pressure is high, headstraps or other mask restraints must be tightly fastened. This produces high localized pressure on the face, not only in the zone of the mask seal but at various locations along the extent of the retention straps as well. This too will result in severe discomfort for the user after only a brief time. Even in the absence of excessive localized pressure points, the tight mask and headstraps often may become extremely uncomfortable and user discomfort may well cause discontinued cooperation with the regimen.
Examples of respiratory masks possessing continuous cushion sealing characteristics of the type just described are provided in U.S. Pat. Nos. 2,254,854 and 2,939,458.
A second type of mask, which has been used with a measure of success, incorporates a flap seal of thin material so positioned about the periphery of the mask as to provide a self-sealing action against the face of the user when positive pressure is applied within the mask. In such a mask, the flap seal typically defines a contoured sealing surface adapted for confronting and sealing engagement with the user's face. Under the influence of a flow of pressurized gas supplied to the interior of the mask which impinges upon the surface opposite the contoured sealing surface, the sealing surface is urged into sealing contact with the user's face. With this type of sealing action, the forces which serve to hold the mask in confronting engagement on the face of the user are much lower than with the first type of mask described above. If the flap seal is capable of conforming to the contours of the user's face without forming leak paths, the mask can be used with retention straps which exert little or no net force to push the mask against the user's face. Thus, the overall sensation of constraint and confinement is dramatically reduced for the user. Such a mask, when properly adjusted, can be adapted to any positive internal mask pressure. The sealing flap will be self-sealing as long as there is no looseness in the strapping arrangement which would allow the mask to move away from the face further than the reach of the sealing flap when subjected to internal pressure.
Among the potential limitations of the second described masked type are two of note. First, the sealing flap seals by laying flat against the user's face throughout its length. This action requires a close match between the contours of the face and those of the seal. If the match is not good, the seal will be ineffective. Secondly, the normal response of one applying the mask to a user's face is to push the mask harder against the user's face if the mask does not seal. With the typical flap seal-type mask, increasing contact pressure against the user's face will not help to form an effective seal if the flap seal does not initially fit well to the facial contours. It may, however, lead to patient discomfort and other problems as described above.
Some of the principal problems one encounters when trying to apply the self-sealing flap concept to the design of the respiratory mask are related to the location of relative low points and high points in the facial contours of the user relative to the shape or contour of the flap seal surface. If the seal surface does not contact the user's face at the relative lower points, then excessive gas leakage will occur thus preventing sufficient internal gas pressure to develop to activate the sealing action of the seal flap at the low points. In the prior art, this problem has been solved for some applications by providing a variety of masks with differing seal flap shapes, sizes and contours. For example, for aircraft breathing masks, especially where expense is not a critical factor, wide variety of mask shapes and sizes may be provided to give the individual users an opportunity to find a mask offering good fit. In other breathing mask applications such as clinical use, where economic considerations may dictate a mask having the capability to accommodate a wide variety of facial sizes and contours, prior flap type seal structures have not generally been able to provide the requisite versatility.
A related problem with flap seal mask structures concerns the high points of the user's face, where the seal flap may tend to distort or collapse and fold in on itself, thus creating a channel for gas leakage, when pressure is applied in order to effect a seal at adjacent relative low points on the user's face. Even where the section thickness of the seal flap is very thin, and the material is very soft and flexible, the internal gas pressure cannot overcome some such seal flap distortion to provide the desired self-sealing.
A mask of the above-characterized flap seal type is described in U.S. Pat. No. 4,907,584, the disclosure of which is incorporated herein by reference. The mask disclosed therein includes a generally annular seal comprised of a peripheral sidewall having an inturned flexible flap seal adjacent a free end thereof, with the inturned seal being configured for confronting sealing engagement with a user's face as above described. Spaced about the peripheral seal wall are plural, upstanding, flexible ribs which serve to support the peripheral wall and an inturned portion of the seal member located generally outward of the face-engaging surface portion of the seal flap. The described seal structure is intended to permit the flap seal and peripheral sidewall to distort without experiencing any mode of seal defeating deformation such as crimping, buckling, folding or other modes of collapse. In this seal structure, the structural support ribs are located and configured in a manner to provide adequate seal flap support where seal deformation is not required (i.e., at the "low" points of the contours of the user's face) and to resiliently deform in a manner to permit easy and uniform distortion of the seal flap in those areas where distortion is necessary to accommodate "high" points on the contours of the user's face.
Other respiratory masks having flexible flap facial seats are disclosed in U.S. Pat. Nos. 4,167,185 and 4,677,977. Masks comprising both continuous cushion and flexible flap sealing features are described in U.S. Pat. Nos. 2,931,356, 3,330,273, and 4,971,051.
Despite its general efficacy in affording a desired seal against the typical user's face, the construction of the inturned flexible flap is such that the contours of certain users' faces may preclude reliable sealing by masks of this type. In this regard, the seal flap includes an opening having an enlarged lower portion to accommodate lower regions of the user's nose (and possibly the user's mouth) and an upwardly extending narrow slot portion adapted to receive the bridge of the nose. The slot bifurcates the flap into a pair of opposed flap portions adapted to lie against opposite sides of the user's nose during use. However, the front portion of the nose is left uncovered and shape of the user's nose may be such that is does not mate particularly well with the slot. For instance, the flap portions may not fully contact the sides of the user's nose or may be excessively displaced thereby which, in either case, may result in leaks in the flexible seal in the region of the nasal flap portions.
U.S. Pat. No. 4,167,185 teaches a flexible flap type mask seal which incorporates reinforcement webs or struts in the nasal flap portions of the seal to force the flap portions against the bridge of the user's nose during use. This arrangement, however, exerts localized pressure on the user's face which, in turn, results in increased user discomfort. Moreover, such a mask seal, like that proposed in U.S. Pat. No. 4,907,584, leaves the front portion of the nose fully exposed and uncovered by any sealing elements, thereby creating another potential avenue of escape for the pressurized respiratory gas.
U.S. Pat. 4,655,213 and Published PCT Application No. WO 82/03548 each describe nasal masks which substantially envelop the user's nose and provide a continuous cushion type perimetrical seal therearound. Such perimeter seals are required because the mask seal bodies are oversized to accommodate but not contact the user's nose. The seals provided by these masks are thus ccnceptually similar to and suffer from essentially the same drawbacks as the continuous cushion type mask seals discussed at the outset.
An advantage exists, therefore, for a respiratory mask facial seal that affords an effective yet comfortable seal for all users, notwithstanding the size and/or shape of a particular user's nose.